/*
 * Copyright (C) 2011 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
 * in compliance with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License
 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the License for the specific language governing permissions and limitations under
 * the License.
 */

package com.google.common.base;

import com.google.common.annotations.GwtCompatible;

import java.io.Serializable;
import java.util.Iterator;
import javax.annotation.CheckForNull;

import org.checkerframework.checker.nullness.qual.Nullable;

@GwtCompatible(serializable = true)
@ElementTypesAreNonnullByDefault
final class PairwiseEquivalence<E, T extends @Nullable E> extends Equivalence<Iterable<T>>
        implements Serializable
{
    final Equivalence<E> elementEquivalence;

    PairwiseEquivalence(Equivalence<E> elementEquivalence)
    {
        this.elementEquivalence = Preconditions.checkNotNull(elementEquivalence);
    }

    @Override
    protected boolean doEquivalent(Iterable<T> iterableA, Iterable<T> iterableB)
    {
        Iterator<T> iteratorA = iterableA.iterator();
        Iterator<T> iteratorB = iterableB.iterator();

        while (iteratorA.hasNext() && iteratorB.hasNext())
        {
            if (!elementEquivalence.equivalent(iteratorA.next(), iteratorB.next()))
            {
                return false;
            }
        }

        return !iteratorA.hasNext() && !iteratorB.hasNext();
    }

    @Override
    protected int doHash(Iterable<T> iterable)
    {
        int hash = 78721;
        for (T element : iterable)
        {
            hash = hash * 24943 + elementEquivalence.hash(element);
        }
        return hash;
    }

    @Override
    public boolean equals(@CheckForNull Object object)
    {
        if (object instanceof PairwiseEquivalence)
        {
            PairwiseEquivalence<?, ?> that = (PairwiseEquivalence<?, ?>) object;
            return this.elementEquivalence.equals(that.elementEquivalence);
        }

        return false;
    }

    @Override
    public int hashCode()
    {
        return elementEquivalence.hashCode() ^ 0x46a3eb07;
    }

    @Override
    public String toString()
    {
        return elementEquivalence + ".pairwise()";
    }

    private static final long serialVersionUID = 1;
}
